It is important to be able to locate and track items, especially as they travel between places. Objects may travel within a single facility or move over greater distances or even transit between countries over land, sea and air. Such items may include freight, post, documents and individual parts of vehicles such as ships, trains and aircraft, for example. Passive electronic tags (e.g. RFID tags) may be attached to individual items so that they may be uniquely identified and interrogated locally at distances of between several millimetres and perhaps up to ten metres. Typically, tags are passive and have no stored electrical energy and so derive their required electrical power from an interrogating signal generated by a tag reader. Therefore, items and goods may be tracked as they pass particular points on a journey or between locations, provided that they pass sufficiently close to a tag reader (i.e. within a short interrogation and reception range). This can work well for freight, which has to follow a particular route with well-defined stops or freight depots. However, for items that travel on less defined routes or that do not have a particular end destination (e.g. parts of aircraft that are in constant use within the aircraft) then passive tags have drawbacks.
Active tags that carry their own power supply can be used to track larger items, such as freight containers. Such tags may have a large battery, a long-range wireless interface (e.g. a GSM radio or satellite communicator) and a position locator such as GPS or GSM triangulation unit. However, once the battery is exhausted then the tag ceases to function and the item will no longer be locatable. Furthermore, such tracking devices are only suitable for larger items due to their size and bulk.
US 2010/0079238 describes an RF-based tag that includes non-volatile memory and a piezo electric sensor. The piezo electric sensor produces an electrical charge that momentarily supplies electrical power to the tag when subjected to a mechanical force. This electrical power is sufficient to record data in the non-volatile memory. Therefore, such a tag can record events that occur during a journey and the non-volatile memory can be read at the end of such a journey to provide additional information. However, such a tag cannot be used to locate items at longer distances.
It is often important to be able to locate individual parts of a vehicle, such as an aircraft. For example, should an aircraft be leased then certain parts may be swapped or replaced during the leasing period. When the aircraft is returned to its owner, then all of the parts must be accounted for. This can be important for regulatory and safety purposes or to audit the number of hours that particular parts have been used so that they can be replaced or serviced appropriately. Furthermore, it can be found that parts are swapped between individual aircraft within a fleet. When those aircraft are returned to their owner or passed on to a new carrier, then again, the original parts must be returned to the original aircraft. In order to track such movements and changes, then significant effort and paperwork may be required to locate missing or moved parts.
Similarly, valuable items such as jewellery and important documents may be transported and moved in use. It is usually not feasible to provide such small items with active global tracking systems due to the added bulk. However, small but valuable items can be lost or misplaced more easily and so it is useful to know their whereabouts at any given time, which is not currently feasible.
Therefore, there is required a method and system that overcomes these problems.